[179] The slow pace of
aeronautical development during the first half of the 1920's was
briefly mentioned in chapter 3. If anything, technical advancements in flying-boat
design during this period lagged behind [180] those of
contemporary landplanes and did not experience the rapid
acceleration that characterized landplane developments in the
latter half of the decade. The biplane configuration dominated
flying-boat design, and most efforts were aimed toward military
applications. In the following section, developments in Navy
patrol boats are discussed, after which two significant amphibian
aircraft developed in the 1920's are described.

The Refined Patrol Boat

According to reference 118, the United States Navy had an inventory of 1172
flying boats at the termination of hostilities in November 1918.
By the middle of 1925, this number had shrunk to 117 aircraft
consisting of outdated wartime H-16, HS-2L, and F-5L boats.
Fortunately, the stagnation in military flying-boat development
was relieved, to some extent, by the Naval Aircraft Factory, which
continued design refinement of the biplane flying boat. The
wartime F-5L, redesignated PN-5, formed the starting point of
these activities, which resulted in a number of improved aircraft
designs. Until 1928, prototypes of each of the improved designs
were built in the limited facilities of the Naval Aircraft
Factory, but lack of funds prevented placing production contracts
with industry.

One prototype, the PN-9, was a much
refined development of the PN-5 equipped with Packard engines and
a hull of aluminum alloy construction. This aircraft achieved a
dubious place in aviation history by its failed attempt to fly
nonstop from San Francisco to Hawaii. With a crew of five under
the command of Commander John Rodgers, the PN-9 left San Francisco
on August 31, 1925, and came down at sea after flying 1841 miles,
a new distance record, about 200 miles short of Maul, Hawaii. A
higher than expected fuel consumption, coupled with the lack of
anticipated tail winds, resulted in fuel exhaustion and the
unanticipated landing at sea. Crude sails were fashioned from
fabric torn from the lower wings, and the flying boat was
literally sailed 450 miles to the Island of Kauai, which was
sighted on the 10th of September. (Marginal steering capability
prevented the aircraft from reaching the much nearer island of
Maui.) Whatever may have been lacking in flight planning or in
understanding of engine performance, the seaworthiness of the new
all-metal hull and the seamanship of the crew were clearly
demonstrated by this remarkable venture. Reference 80 is cited for a succinct description of the
flight.

By 1928, the Navy had both a flying-boat
design that it liked, the PN-12, and sufficient money to place
production contracts with several [181] aircraft
manufacturers. Martin, Douglas, Keystone, and Hall Aluminum
ultimately participated in the program, and aircraft produced by
these companies were designated PM, PD, PK, and PH, respectively.
The aircraft produced by each company were based on the
Navy-designed PN-12, but they differed from this aircraft and from
each other in a number of details that are not discussed here.
Detailed descriptions of each of the aircraft can be found in
references 109 and 118.

Typical of the patrol boats produced in
this program was the Martin PM-1 illustrated in figure 8.8. The
aircraft had the classic twin-engine biplane configuration,
similar in concept to the F-5L, but was much cleaner than the
earlier aircraft. The number of drag-producing interplane struts
and wires had been reduced, and the tip-bracing arrangement on top
of the upper wing had been eliminated. Neatly cowled nine-cylinder
radial air-cooled engines on the PM-1 contrasted with the exposed
in-line engines and clumsy radiators on the F-5L. The data in
table
IV show that the PM-1 had more
power, was somewhat heavier, and had slightly less wing area than
the F-5L it was designed to replace. The Martin, however, was
nearly 30 miles per hour faster than the earlier aircraft and had
a 31-percent lower zero-lift drag coefficient. The higher value of
the lift-drag ratio of the F-5L resulted from the higher wing
aspect ratio of this aircraft as compared with the PM-1. The lower
aspect ratio of the Martin boat probably resulted from a design
trade-off between aspect ratio and empty weight, in....

[182]....combination
with the effect on CD,O of more
interplane bracing which would probably have been required for
higher aspect ratio wings. The hull of the PM-1 was a refined
version of the sponson-type, two-step employed on the F-5L and was
of all-metal construction; the wings were of metal-frame structure
covered with fabric and had thicker airfoil sections than those
used on the F-5L.

Flying boats based on the PN-12 design,
such as the PM-1, served the Navy until well into the 1930's. The
U.S. Coast Guard also employed these aircraft and ordered several
of those produced by the Hall Aluminum Company, the PH-3, as late
as 1938.

The last and also the largest and highest
performance biplane flying boat developed for the U.S. Navy was
the Hall XP2H-1 shown in figure 8.9. (The largest biplane flying
boat ever built was the Short Sarafand launched in England in
1932. It had a gross weight of 70 000 pounds, a wing span of 150
feet, and was equipped with six engines, mounted pusher-tractor
style in three nacelles, totaling 5500 horsepower. The Sarafand,
after service with the Royal Air Force, was scrapped in 1936.) The
XP2H-1 was equipped with four in-line Curtiss V-12 engines of 600
horsepower each; the engines were configured in a ....

[183] ...
pusher-tractor arrangement in two streamlined nacelles mounted
atop support pylons. The wings of the single-bay biplane were
tapered, had a metal internal structure covered with metal sheet,
and were braced with struts and wires. The single-step hull was of
all-metal construction and had enclosed accommodations for the
crew of six. Figure 8.9 shows a complex tail assembly featuring
two fins and rudders mounted on top of a single horizontal
surface, which in turn was attached to the hull by a single,
low-aspect-ratio fin or pylon.

The data in table IV give a gross weight of 35 393 pounds for the XP2H-1
and a maximum speed of 139 miles per hour. The zero-lift drag
coefficient of 0.0291 was about 40 percent lower than that of the
Martin PM-1, and the maximum lift-drag ratio of 10.2 was about 30
percent higher than that of the Martin PM-1. At a much reduced
speed, maximum endurance could be obtained by cruising on two
engines, and the maximum range was estimated to be 4560 miles.
Although the Hall XP2H-1 had very creditable performance, it
arrived on the scene too late to compete effectively with the new
monoplane flying boats that began to appear in the 1930's.

Ordered in 1930 and delivered to the Navy
in the fall of 1932, the XP2H-1 was a one-of-a-kind aircraft. In
25 hours and 15 minutes, the aircraft made a notable nonstop
flight from Norfolk, Virginia, to Panama in 1935. The pilot on
this flight was Lt. John S. Thatch, who was destined for fame in
World War II. The aircraft met an ignominious end later in 1935
when it sank during an open-sea landing attempt. The XP2H-1
represents the last in a long-lived line of United States designed
biplane flying boats.